This invention relates to a projection exposure apparatus and a device manufacturing method using the same.
In projection exposure apparatuses for use in the manufacture of semiconductor devices, for example, higher resolution has been required to meet enlargement of integration of VLSI. In this stream, ultra-resolution technology using an oblique incidence illumination method or a phase shift mask has been proposed. In such ultra-resolution technology, the aperture stop of an illumination optical system is modified to make smaller the "sgr" value (the ratio between the NA (numerical aperture) of a projection optical system and the NA of the illumination optical system), or a secondary light source of a peculiar shape such as a ring zone shape or quadrupole shape, for example, is defined.
Also, in projection exposure apparatus for semiconductor device production, generally the optical arrangement is telecentric on the image side so that there occurs substantially no deviation of the position of a projected pattern image even if a substrate such as a wafer is at a defocused position.
In the stream of larger integration of recent VLSI, a very high transfer precision is required for printing of a circuit pattern. It is, therefore, very important to properly set the angular distribution of illumination light, entering a projection optical system. If illumination light with a predetermined angular relation with respect to the projection optical system is not supplied, then a positional deviation occurs in the position of a projected pattern image on an occasion when the wafer is at a defocused position.
When a wafer is defocused and a pattern is printed, a deviation in incidence angle of illumination light in magnification relation with the optical axis center, with respect to a projection optical system (i.e., deviation of incidence angle of each light ray with respect to the projection optical system, according to the distance (object height) to the optical axis), causes a positional deviation in magnification component corresponding to the image height, in the printed pattern. This deviation is referred to as magnification telecentricity or deviation of magnification telecentricity. FIG. 2 illustrates this, wherein broken lines denote an optical axis or a line parallel to it.
In FIG. 2, denoted at 16 is a projection optical system, and denoted at 18 is a substrate (wafer). Denoted at La is the optical axis of the projection optical system 16. A shift or deviation of incidence angle of illumination light with respect to the projection optical system, with which chief rays are inclined in the same direction regardless of object height, causes a shift or deviation of a printed pattern when the wafer 18 is defocused (this deviation is referred to as an on-axis telecentricity or deviation of on-axis telecentricity). FIG. 3 illustrates this, wherein broken lines denote an optical axis or a line parallel to it.
This means that images are printed with deviation when, during the procedure of plural lithographic processes, circuit patterns are to be superposedly printed on a wafer having surface steps formed thereon. It is very undesirable for production of high precision semiconductor devices.
In many projection exposure apparatuses, positions of components of an illumination system are adjusted so that it provides illumination light with an angular characteristic best for a certain standard illumination mode A. However, when the illumination mode A is changed to a different illumination mode B (such as for oblique incidence illumination or smaller "sgr" value), the components of the illumination system, if they are unchanged as in the illumination mode A, do not always provide illumination light with a proper angle. This is because the optical path is different between these illumination modes and also the effect of eccentricity of a lens system or non-uniformness of an anti-reflection film of an optical element differs.
In projection exposure apparatuses, the effect of an anti-reflection film used for an optical element differs with the angle of a light ray. Thus, when the illumination mode is changed, there may occur a deviation of magnification telecentricity. Similarly, when the illumination mode is changed, the effect of reflection non-uniformness at deflection by a mirror or the effect of eccentricity of an optical system changes. Thus, there may occur a deviation of on-axis telecentricity.
If such magnification telecentricity or on-axis telecentricity is corrected by moving the optical system, it causes a change in illuminance distribution on the surface to be illuminated (such as a reticle surface or wafer surface), thus enlarging illuminance non-uniformness. It is not easy to correct both of them in conventional exposure apparatuses.
It is an object of the present invention to provide a projection exposure apparatus by which, based on correction of magnification telecentricity deviation, illumination light can be supplied with an optimum angle such that a pattern image can be formed with a very high resolution.
It is another object of the present invention to provide a device manufacturing method using such a projection exposure apparatus.
In accordance with an aspect of the present invention, there is provided a projection exposure apparatus having an illumination optical system for illuminating a reticle having a pattern, a projection optical system for projecting the pattern onto a substrate, and measuring means for measuring an angular distribution of illumination light, wherein an optical element in a portion of said illumination optical system is displaced along an optical axis direction on the basis of a measurement result of said measuring means, to change the angular distribution of the illumination light entering the projection optical system, with magnification with respect to the optical axis center.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.